Thermally directed glass cutting

ABSTRACT

This invention relates to a method and apparatus for cutting glass wherein glass is thermally scored along an intended path of cut, using a non-radiant, surface heating means. A fracture is then directed along the intended path by applying a bending moment about the thermal score.

United States Patent 1 Dahlberg et al.

THERMALLY DIRECTED GLASS CUTTING inventors: John R. Dahlberg, Jeannette;James L. Oravitz, Cheswick; Edmund R. Michalik, West Mifflin, all of Pa.

Assignee: PPG Industries, Inc., Pittsburgh, Pa.

Filed: June 21, 1972 Appl. No.: 265,080

Related US. Application Data Division of Ser. No. 72,354, Sept. 15,1970, Pat. No. 3,730,405.

U.S. Cl 65/112, 65/176, 225/2, 225/93.s, 225/96.5 Int. Cl C03b 33/02Field of Search..... 65/112, 113, 174, 175, 176; 225/93.5, 96.5, 2;219/381 Feb. 19, 1974 [56] References Cited UNITED STATES PATENTS3,587,956 6/1971 Oelke 225/93.5 3,371,188 2/1968 Henes et al. 3,695,49810/1972 Dear 225/1 UX Primary ExaminerArthur D. Kellogg Attorney, Agent,or FirmThomas F. Shanahan [57 ABSTRACT This invention relates to amethod and apparatus for cutting glass wherein glass is thermally scoredalong an intended path of cut, using a non-radiant, surface heatingmeans. A fracture is then directed along the intended path by applying abending moment about the thermal score.

5 Claims, 3 Drawing Figures THERMALLY DIRECTED GLASS CUTTING This is adivision, of application Ser. No. 72,354, filed Sept. 15, 1970 now U.S.Pat. No. 3,730,408.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to a method and apparatus for severing glass sheets by applyingheat only to the glass surface along an intended path of cut andapplying a bending moment about said path.

2. Description of the Prior Art The most pertinent prior art of which weare aware comprises Campbell et a]. U.S. Pat. No. 1,720,883; Hitner,U.S. Pat. No. 1,777,644; Spinasse, U.S. Pat. No. 1,973,546; Kovacik etal., U.S. Pat. No. 3,344,968; and Hafner, U.S. Pat. No. 3,453,097.

The Campbell et al. patent discloses, for example, the severing of glassin accordance with a method comprising bringing a hot object or objectsor elements, heated electrically or otherwise, into contact with or intoclose proximity of the glass. It discloses, moreover, that: In order toquickly initiate the severing action, a nick or fault or other weakenedportion may be formed by the apparatus at a point on the glass at theline of cleavage where the severage action is to start.

The Hitner patent discloses, for example, an improved apparatus adaptedto prevent the somewhat irregular line of fracture which has hithertobeen characteristic of the severing of glass by the use of anelectrically heated wire or ribbon." This patent uses an electricallyheated wire for the non-contact severing of glass, but it teachesproviding means for giving a distribution of heat over a substantialarea of glass on each side of the ribbon or wire," stating that as aresult, the line of fracture is smooth and regular, approximating inthese particulars the line of fracture secured by scoring the glass witha diamond or wheel.

The Spinasse patent discloses, for example, a tubular portion of metalor other suitable refractory material adapted to present a heatingsurface in close contact with or in close proximity to the body of thedrawing sheet near the region where the same is to be cut to remove theborder. It further states: It will be obvious, therefore, that as asheet of glass is drawn past the heating element the border of the glassis heated in a path parallel to and near the edge of the sheets so thatif the glass could be cut or checked by means of a cold checking toolbeyond the heated path, shown by the broken line in FIG. 2, the bordercan be easily removed without fracturing the body of the sheet.

Kovacik et al. disclose, for example, A plurality of spaced score lines20 to 23 are made on one surface of the sheet inwardly of eachlongitudinal edge and thereafter the portions A, B and C arerespectively or successively removed to redistribute the stresses withinthe glass sheet. The final cut is then made by locating the gauging bara distance of one-half the width of the heating apparatus from thepredetermined line of cut 23 and thereafter aligning the heatingapparatus against one surface of the gauging bar to locate theelectrical resistance element on the score line 23. Heat is supplied asufficient period of time to allow the cut to run the entire length ofthe sheet.

The H'zifner patent discloses, for example, a method of cutting glasswherein the glass sheet is moved continuously past a continuous laserbeam which is focused upon the glass sheet. The laser and absorptivecharacteristics and parameters are selected but the glass absorbs thelaser energy and converts it into sufficient heat to enable theseparation of the sheet into pieces along the line swept by the laserbeam."

SUMMARY OF THE INVENTION In accordance with this invention, a piece ofglass is severed by:

a. inducing an artificial defect in an edge area of the piece along anintended path of cut;

b. providing an in-line array of hot-gas heaters aligned with the path;

c. heating the piece only on a surface in the vicinity of the intendedpath by activating said heaters; and

d. applying a bending moment about the path to sever the piece.

The artificial defect is not an essential feature of the invention but,when used, it does provide higher quality edges. It is normally an edgenick or a surface score (fracture-initiation score) about one-fourthinch to one-half inch in length that is applied to the glass by anoperator using a hand tool. It is important to note that this edge nickcan be placed on the glass either before or after the sheet is exposedto the array of heaters, as long as the nick is placed on the glassprior to the application of the bending moment. If the edge nick isomitted, the fracture will often run out (not follow the intended pathof cut) at the ends.

The method of the present invention can be performed on plate glass,float glass, sheet glass and lowexpansion glass, with edges beingproduced, in each instance, that are straight, smooth, strong andperpendicular to the surfaces of the glass.

The present invention is of great importance in connection with thesevering of sheets that are greater than 0.25 inch in thickness becausewhen mechanicalscoring means have been used in connection with theabove, there has hitherto been difficulty in obtaining a cut edge ofsatisfactory appearance, high edge strength, and other desirablecharacteristics. It has been particularly difficult to obtain, incutting a piece of glass that thick, an edge that is suitable forfurther use without a further grinding or polishing operation. Moreover,the strength of the cut edge produced by prior-art methods such as handscoring and snapping usually does not exceed 3,900 pounds per squareinch and is frequently considerably less than that, whereas it isfrequently desired that, especially without such grinding and polishing,the cut edges exhibit better edge-strength values. The present inventionis of particular importance in the severing of glass sheets that arebetween about 0.50 inch and 0.75 inch in thickness, and even thicker.

Edges produced by any of the thermal severing methods recently developed(see U.S. Pat. application Ser. No. 66,940, filed Aug. 26, 1970, nowallowed as U.S. Pat. No. 3,595,497; U.S. Pat. application Ser. No.66,941, filed Aug. 26, 1970 now allowed as U.S. Pat. No. 3,695,498; andcopending U.S. Pat. application Ser. No. 72,353 now U.S. Pat. No.3,709,414, filed Sept. 15, 1970) have a pristine appearance and highstrength. The problem in applying any of these thermalseveringtechniques to production cutting has been the inability to achievedirectional control on nonbisecting cuts. Recent work by us has revealedthat when using an infrared thermal source on trim cuts, the

temperature profile about the intended path of cut is not symmetrical,with the trim side being slightly warmer. It has been proposed to usedirectional controls such as heat shields in conjunction with aninfrared source to produce straight, non-bisecting cuts. Heat shields donot appear to be an ideal solution in that they require a large supplyof shields be on hand (one for each length of cut).

It is an object of the present invention to provide an edge that isstraight, smooth, strong and perpendicular to the surfaces of the glassand yet one that requires no exterior directional controls in itsmanufacture.

It is a further object of this invention to provide a method and meansfor severing a glass sheet wherein only the surface of said sheet isheated. This eliminates the adverse effect of the trim edge which causesan asymmetrical temperature profile when the glass is heated through itsthickness, as by an infrared source.

In a preferred embodiment, this invention employs the use of an in-linearray of hot-gas heaters, so that only the glass surface is heatedrather than the surface and the interior, as is the case when usinginfrared heat or a gas flame. In this preferred embodiment, a fractureinitiation score of from one-fourth to one-half inch is placed on a topsurface of the leading edge coinciding with the intended path of cut.Relative motion is effected between the glass and the in-Iine array ofheaters, which are nozzled and focused close to the glass to impart anarrow thermal score along the intended path of cut. The leading edge ofthe glass is then moved into a finger snapper, which exerts an openingbending moment on the glass. The fracture originates at thefracture-initiation score and follows the thermal score across theplate. Trim cuts made in this manner follow the intended path of cut.

As used in this application, the terms thermal score and thermal scoringdo not mean a scratch or groove in the glass surface, but rather acondition brought about by surface heat wherein stresses are createdthat extend from one surface to an opposite surface of the sheet ofglass. The term satisfactory thermal score" means a thermal score whichhas weakened the glass to such an extent that a bending moment appliedabout the score will fracture the glass and leave a high-quality edge.

Distinct advantages are obtained by conducting the cutting in the mannerherein taught. In general, when the cutting is done in the manner taughtin accordance with this invention, the edge strength of the cut piece isabout at least twice that of a piece cut in accordance with prior-artmethods such as hand-scoring and snapping. The increase in edge strengthis not merely of academic interest, since the edge strength is relatedto the observed incidence of breakage during any subsequent handling ofthe edge-cut sheet of glass involved.

DESCRIPTION OF THE DRAWINGS A complete understanding of the inventionmay be obtained from the foregoing and following description thereof,taken in conjunction with the appended drawings, in which:

FIG. 1 is a schematic elevation view of equipment used in accordancewith the present invention;

FIG. 2 is a view, drawn to scale, of a heater used in accordance withthe present invention; and

FIG. 3 is a view indicating the practice of applying a bending momentabout the thermal score.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there isshown a piece of glass G resting on a carriage 10 that has wheels 12which allow the carriage to move on work table 14. As carriage 10 ismoved in the direction of arrow 16, glass G passes beneath an in-linearray of heaters 18 which are mounted on table 14 by means of a frame 20and are spaced about one inch apart, one from another. In thealternative, it is also possible to keep the glass G stationary and moveheaters 18. Any arrangement that provides relative movement between theglass G and the heaters 18 is sufficient.

As the glass passes beneath the heaters 18, a thermal score is createdin the glass along an intended path of cut. This creates a shallowtensile stress field within the glass, so that a bending moment may beapplied about the thermal score to create a fracture, leaving an edgethat is strong, straight, smooth and perpendicular to the surfaces of aglass.

The present invention relies on hot-air or hot-gas heaters to providenon-radiant energy and produce quality edges in both bisecting andnon-bisecting cuts. In accordance with the present invention, only thesurface of the glass is heated. This is different from the prior methodswhich use an infrared source to heat the glass throughout its thickness.Using the hot-gas heaters of the instant invention eliminates theproblem of trim or non-bisecting cuts, since it eliminates internalreflections which cause asymmetrical temperature profiles.

Referring to FIG. 2, there is shown a gas heater l8, drawn to scale,comprising a quartz tube 22 mounted within one end 26 of a siliconerubber grommet 24. Mounted within the other end 28 of grommet 24 is aplastic tube 30, which supplies the gas to the heater. The other end ofthe tube 30 is attached to any suitable gas supply, such as the manifoldillustrated at 31 in FIG. I. Mounted within quartz tube 22 is a filament32 of tungsten or a ferrous alloy or of any other suitable material. Atthe interior end of the filament 32 on grommet 24 are two electricalconnections 34 and 36, which are used to attach wires or conductors 38and 40 to the filament 32. Wires or conductors 38 and 40 are connectedat their other ends (not shown) to a suitable source, such as one ofvolt, 6O cps.

At the end of tube 22 there is a nozzle 44 that is approximately oneinch in length and has an opening between about 0.060 and 0.075 inch.Adjacent to nozzle 44, the tip 46 of the filament 32 heats the air orgas within the tube so that it is between about l,700 and 2,200F andperhaps higher.

It is recognized that gas heaters per se are old, and applicants do notclaim to have invented a gas heater. Rather, the invention hereinresides in using an in-line array of gas heaters for the severing ofglass. Suitable gas heaters are manufactured by Sylvania, a subsidiaryof General Telephone and Electronics, such as their Model No. 114682.

Successful thermal scoring is a function of the following factors: (a)air temperature, (b) focal distance, (c) number of heaters, (d) scanspeed, (e) glass thickness, (f) length of cut, (g) width of trim, and(h) the length of time between the start of heating and the running ofthe fracture.

The temperature of the air or gas at tip 46 is normally between aboutl,700 and 2,200F. Higher temperatures permit faster scan speeds. With agas temperature of l ,700F at the tip 46, the gas temperature at theglass surface is about 900F and the temperature of the glass at thesurface is about 200F.

It has been found that there should be about 0.05 to 0.10 inch betweenthe glass surface and the tip of the heater. If the heater is movedcloser than about 0.05 inch, drag is created and the cut becomes lesspractical. If the heater is moved farther away, there is a resultantheat loss at the glass surface.

The number of heaters is an important consideration in the presentinvention. As the glass thickness increases, more heat is necessary (andtherefore more heaters) to produce a thermal score that will cause thebending moment to sever the glass along the score. For glass that isone-half of an inch in thickness, five heaters produce a thermal scorethat yields a high quality edge. When the number of heaters isincreased, the scan speed can be increased. For glass that isthreequarters of an inch in thickness, five heaters do not yield enoughheat to produce a satisfactory thermal score, no matter how slow thescan speed. When five heaters are used on A-inch glass, the fracturepropagation does not follow the thermal score. It has been found that anin-line array of eight heaters produce a satisfactory thermal score on%-inch glass. With lower scan speeds, perhaps seven or maybe even sixheaters arranged in line could be used to produce a satisfactory thermalscore. I

The speed with which the array of in-line heaters scans the glass isdirectly related to all of the other factors. Generally, thicker glassrequires lower scan speeds.

The length ofa trim cut does not in itself have any effect on thethermal score except for the fact that with a long cut, the time betweenthe application of the heat and the running of the fracture bymechanical snapping becomes farther apart. Therefore, with longer trimcuts, more energy must be put into the thermal score so that the bendingmoment can be applied before the heat has been dissipated from the pieceof glass and the thermal score has decayed.

Generally, narrower trims require slower scan speeds. This is probablydue to the stronger gradient adjacent to the edge. To get some idea ofthe effect of trim width on scan speed, consider that for /2-inch glass,scan speed varies from about 150 inches per minute to about 450 inchesper minute as trim width varies from 4 inches to 11 inches.

Using eight hot-air heaters of the kind illustrated in FIGS. 1 and 2,spaced 1 inch apart one from another in an in-line arrangement, eachoperating at 460 watts with an air temperature of 1,700F at the tip 46,a scan rate of 121 inches per minute will produce a satisfactory thermalscore for removing a trim 4 inches by 24 inches from a piece of clearfloat glass 6 inch of 24 inches by 36 inches. Using the same heaterarrangement, a scan rate of 82 inches per minute produces a satisfactorythermal score for removing a trim 6 inches by 31 inches from a piece ofclear float glass inch by 19 inches by 31 inches.

It is important that an edge nick (fracture-initiation score) be appliedto an edge of the glass surface along the intended path of cut, eitherimmediately before or immediately after the thermal score is applied tothe glass surface. Referring to FIG. 3, there is shown a'diagram of asnapper 48, applying a bending moment about the thermal score after theartificial defect 50 has been made. Actually, any conventional snappingmeans may be used.

The application of the bending moment must be about the thermal score,which must pass through the edge nick for a high-quality edge to result.If the edge nick is omitted or if the bending moment is not applied Iabout the thermal score, or if the moment is not applied within about 15seconds, the resulting edges may have defects, such as lack ofsmoothness, lack of perpendicularity to the glass surfaces, lack ofadequate edge strength, and lack of straightness.

I claim:

1. A method of thermally scoring a piece of glass along an intended pathof cut so as to permit the severance thereof along said path comprisingthe steps of:

aligning at least one hot-gas heater with said path,

convectively heating a narrow zone on a surface of said piece along saidpath by activating said heater, said convective heating being at atemperature and for a time sufficient to introduce a thermal stressthroughout the glass beneath said zone without, however, introducingsufficient thermal stress to fracture said glass, contemporaneouslytherewith providing relative movement between said heater and said glassand maintaining said thermal stress in said glass until it is severedalong said intended path of cut.

2. A method according to claim 1 wherein said gas is air.

3. A method according to claim 1 wherein there is provided an in-linearray of hot-gas heaters aligned with said path and said piece is movedrelative to said array of heaters while said piece is heated.

4. A method according to claim 1 wherein said piece .I .l 1 wherein saidpiece I I l to claim 5. A method according is at least about 0.75 inchin thickness.

l l l l

1. A method of thermally scoring a piece of glass along an intended pathof cut so as to permit the severance thereof along said path comprisingthe steps of: aligning at least one hot-gas heater with said path,convectively heating a narrow zone on a surface of said piece along saidpath by activating said heater, said convective heating being at atemperature and for a time sufficient to introduce a thermal stressthroughout the glass beneath said zone without, however, introducingsufficient thermal stress to fracture said glass, contemporaneouslytherewith providing relative movement between said heater and said glassand maintaining said thermal stress in said glass until it is severedalong said intended path of cut.
 2. A method according to claim 1wherein said gas is air.
 3. A method according to claim 1 wherein thereis provided an in-line array oF hot-gas heaters aligned with said pathand said piece is moved relative to said array of heaters while saidpiece is heated.
 4. A method according to claim 1 wherein said piece isat least about 0.50 inch in thickness.
 5. A method according to claim 1wherein said piece is at least about 0.75 inch in thickness.